The present invention relates generally to cannulas for use in laparoscopic surgery and more particularly to a cannula which prevents the escape of gas from a body cavity in which a laparoscopic surgical procedure is being performed.
In performing laparoscopy surgery, an incision is made in a patient to admit a cannula which serves as a conduit for the introduction of minute surgical instruments into the peritoneal cavity. The peritoneal cavity is generally filled with gas to expand the surrounding tissue to create a suitably sized operating space.
During manipulation of the instruments in a surgical procedure, the pressurized integrity of the peritoneal cavity or pneumoperitoneum must be maintained. Therefore, it is necessary that there be a proper seal between the cannula and body tissue at the incision point. To attain this objective, prior art devices have typically employed a conical shaped sealing sleeve which generally is constructed using a rigid material. Upon insertion into the incision, the sleeve's conical geometry pushes or displaces outward the tissue surrounding the incision. The tissue's natural resiliency will then cause the tissue to try to return to the tissue's original position which creates a sealing force against the surface of the sealing sleeve.
However, if there is major movement of the cannula during an operation, the tissue's resiliency may be insufficient to supply an adequate sealing force against the rigid sleeve; therefore, prior devices attempt to maintain the integrity of the seal during the procedure through the use of positioning means so movement of the cannula and sealing sleeve relative to the patient's tissue is reduced. Two devices as disclosed in U.S. Pat. No. 3,817,251 and U.S. Pat. No. 4,985,033 employ hooks or clamps attached to the cannula and the use of sutures to tie these hooks or clamps to a patient's tissue. Another device as disclosed in U.S. Pat. No. 5,002,557 employs an inflatable membrane at the insertable end of the cannula and positions the cannula by capturing a patient's tissue between the sealing sleeve and the expanded membrane. The nature of the laparoscopic procedure however, can require significant reorientation of the cannula during surgery and these prior art devices only tend to minimize relative movement during unintentional reorientation.
Recognizing the possibility of a potentially hazardous loss of the gas tight seal from movement of the cannula or from an uneven sealing force if the shape of the incision does not correspond to the cross-sectional geometry of the sealing sleeve, surgeons typically insert and affix such prior art devices to the patient so there is a significant downward force exerted by the sealing collar on the tissue. Such downward force causes greater displacement of the tissue surrounding the incision thus increasing the range of movement of the sealing sleeve which may be compensated for by the resilient nature of the tissue. This downward force and resulting displacement in turn often results in localized trauma to the tissue. Movement of the cannula during the operation exerts additional force on portions of the incision which can also result in localized trauma.